1. Field of the Invention
The present invention relates to drainage of borders of stabilized civil engineering areas such as roads, airfield runways and railroad tracks, for example, and further relates to drainage of adjacent borders of any structure.
2. Description of the Prior Art
In regard to roads and highways, drainage has always been necessary and is probably even more necessary at the present time on account of rising trends in traffic density as well as in weight of vehicles and also by reason of the periods of exceptional frost which have been observed during recent years. In point of fact, the water content of roads and highways is a determining factor in the stability of road surfaces.
At the present time, the most elaborate technique for draining the sides of a roadway or other stabilized area consists in forming in the ground a narrow trench 15 to 20 cm in width in which is introduced a complex vertical drainage element composed of a water-tight core having a plurality of wavy corrugations or other forms of surface relief, and of an outer jacket of filtering material, the bottom portion of which carries the drainage pipe or water-outflow duct. Thus European patent Application No. 75,993 and French Pat. No. 2,462,518 both describe complex drainage elements of this type which are intended to be used for this purpose.
However, this drainage technique is subject to a certain number of disadvantages. In the first place, it is necessary to dig a trench having a width which is greater than that of the drainage element to be placed in position. This is in fact an essential condition for laying the element by reason of its limited flexibility. In consequence, the excavating and earthmoving operations which have to be performed are as extensive as those required for conventional drainage systems which provide for simple backfilling with filtering materials. Moreover, digging of a trench also results in lateral decompaction of the roadway. Finally, after positioning of the vertical drainage element thus provided, it is necessary to backfill the trench either partially with previously extracted materials or with additional materials which preferably have a filtering function.
A further disadvantage lies in the fact that the complex drainage element thus provided is not capable of complying with the surface irregularities of the trench wall against which it is applied. There consequently remain free spaces produced by inevitable breakaway of certain soil elements during excavation of the corresponding trench. However, the existence of such free spaces is clearly liable to affect the stability of the adjacent roadway.
Yet another drawback of the technique discussed in the foregoing lies in the fact that the majority of complex drainage elements in accordance with this design and arrangement are not provided with a bottom drainage pipe.
Finally, the use of these complex drainage elements proves very costly by reason of a certain number of factors including in particular the mode of manufacture involved by reason of their basic design, the high cost of raw materials employed, the cost of transport of such elements to their place of use and the cost of positioning of these elements.
In regard to the last-mentioned point, it should be borne in mind that the technique under consideration involves the performance of three successive operations: first of all, the formation of a trench of relatively substantial width, then the positioning of the complex drainage element provided and finally backfilling of that portion of the width of the trench which remains free after installation of said element.
For this reason, the object of the present invention is to provide a drainage system of the type considered which is just as efficient as in the case of the technique described earlier but which is not subject to its disadvantages.